Dimensions of the human posterior septal space and coronary sinus.

Accurate anatomic localization of accessory pathways during preoperative electrophysiologic study and during operative mapping depends on a knowledge of the dimensions of the posterior septal space and the left free wall. These dimensions were therefore studied in 48 human cadaver hearts. Mean distance from the coronary sinus orifice to the left margin of the posterior septal space was 2.3 +/- 0.4 cm and mean length of the left free wall was 5.0 +/- 1.0 cm. The posterior septal space at the level of the valve anuli extended a mean of 3.4 +/- 0.5 cm around the epicardium. The width of the posterior septum measured in the coronary sinus was related to heart weight and a combination of body weight and patient age (p less than 0.05). The probability of an accessory pathway being located in the left free wall or the posterior septum during catheter mapping was calculated for various distances from the coronary sinus orifice for adults of different ages and body weights. In adults, accessory pathways located in the proximal 1.5 cm of the coronary sinus are almost always in the posterior septum. Those located between 1.5 and 3 cm from the coronary sinus orifice may be in either the left free wall or the posterior septum, and those located greater than 3 cm from the coronary sinus orifice are almost invariably in the left free wall.